Ion recombination rate constant

Another situation in which an already well-studied proton transfer reaction serves as a probe of a physical phenomenon has been suggested by Knight, Goodall and Greenhow (43, 44). They ionized water with single photons of Nd glass laser infrared radiation and measured an ion recombination rate constant for the reaction... 

An estimate of the electron-ion recombination rate constant in high-mobility systems based on an empirical model of energy dissipation processes was provided by Warman [38]. He related the rate constant to the field dependence of the electron mobility, and proposed... 

Here Tio denotes the critical electric field strength expressed in units of V/m, at which the electron mobility deviates 10% from the thermal mobility, and is used as a measure of the rate of the electron energy dissipation in a particular system. Despite its simplicity, Eq. (40) is shown to give reasonable estimates of the electron-ion recombination rate constant for some of the experimentally studied high-mobility systems. 

The simulation results of the electron ion recombination rate constant obtained in Ref. 39 are plotted in Fig. 5. The figure shows that the rate constant becomes lower than the Debye-Smoluchowski value when the electron mean free path exceeds —O.Olrc. At higher values of X, the ratio kjk further decreases with increasing mean free path. The simulation results are found to be in good agreement with the experimental data on the electron ion recombination rate constant in liquid methane, which are also plotted in Fig. 5. 

The dependence of the electron ion recombination rate constant on the mean free path for electron scattering has also been analyzed on the basis of the Fokker Planck equation [40] and in terms of the fractal theory [24,25,41]. In the fractal approach, it was postulated that even when the fractal dimension of particle trajectories is not equal to 2, the motion of particles is still described by difihsion but with a distance-dependent effective diffusion coefficient. However, when the fractal dimension of trajectories is not equal to 2, the motion of particles is not described by orthodox diffusion. For the... 

Figure 6 Dependence of the electron-ion recombination rate constant on the external electric field F, calculated for different values of the electron mean free time r. The unit of Cis, and that of r is r l k-g,Tlnif. The simulation results of Morgan [45] for liquid methane at 120 K are shown by crosses. (From Ref. 48.)...

In the liquid phase, observed electron-ion recombination rate constants kr in a variety of nonpolar media were, as shown in Fig. 15, in good agreement with the values of k, calculated from the reduced Debye equation,... 

It is important to note that at the low pressures of almost all the earlier studies the total rate constant is effectively only the two body electron-ion recombination rate constant, (012), with little or no contribution from three body effects (ttj). Several hundred Torr of gas pressure are required to clearly distinguish the effects of three-body recombination. In addition, the low values of (< 10 cm s ) measured by many of the early workers were almost... 

Table 11. Temperature dependence of electron-ion recombination rate constants for hydrated hydronium ions Leu et al. [48] in units of 10 cm s ).

Honda, K., Endou, K., Yamada, H., Shinsaka, K., Ukai, M., Kouchi, N., and Hatano, Y., Electron-ion recombination rate constants in gaseous and liquid krypton, /. Chem. Phys.,... 

The conductivity K induced by radiation absorption at dose rate I (eV°=cm-3 s-1) is given by K = uc, where c the is free ion concentration and u is the sum of mobilities of positive and negative carriers. The establishment of steady state requires equal rates of generation and recombination, or IGR /100 = kc2 where k is the second-order recombination rate constant. Eliminating c between these... 

The breakdown of the diffusion theory of bulk ion recombination in high-mobility systems has been clearly demonstrated by the results of the computer simulations by Tachiya [39]. In his method, it was assumed that the electron motion may be described by the Smoluchowski equation only at distances from the cation, which are much larger than the electron mean free path. At shorter distances, individual trajectories of electrons were simulated, and the probability that an electron recombines with the positive ion before separating again to a large distance from the cation was determined. The value of the recombination rate constant was calculated by matching the net inward current of electrons... 

In the gas phase at one to several atmospheric pressures, electron-ion recombination processes have been studied with a pulse-radiolysis method, and observed recombination rate constants kj are expressed by,... 

The measured H atom G-value is about 0.25 at MZ jE = 1, while the equivalent yield of hydrated electrons is found at MZ jE = 10. The persistence of the hydrated electron to higher MZ jE values suggests that it does not decrease to zero at an infinite value of MZ jE. Most H atoms are produced in conjunction with OH radicals in the core of the heavy ion track. The recombination rate constant is high so there is a small probability that H atoms will escape the track at high LET (MZ jE). H atoms can be formed by hydrated electron reactions and their yield cannot decrease to zero if hydrated electron yields do not. However, hydrated electron yields are low at high MZ /E values so the H atom yield can be considered negligible in this region. 

Possible applications of laser enhanced ionization in flame diagnostics are 1. simultaneous observation of ionization and fluorescence signals from various levels might provide more information on the sequence of processes leading to and from the ionization continuum 2. the measurement of ion mobilities, relating to cross-sections for elastic collisions between ions and flame particles 3. measurement of ionization rate constants relating to cross-sections for inelastic collisions between excited atoms and other flame particles 4. measurement of recombination rate constants, relating to cross-sections for inelastic collisions between ions, electrons and neutrals. 

The ion-electron dissociative recombination-rate constant of reaction (42) has been measured 9 and was found to be approximately 4 X 10 7 ion-1 cc. sec."1. 

---